This is nearly always
Black's fourth move in the Sicilian, to force the N on b1 in front
of the c-pawn. Left alone, White may play c2-c4, stopping
counterplay with d7-d5 or b7-b5, and removing danger on the c-file.

Chess magazines are full of quick White kills against the
Sicilian. Why do players bother with it, then? Because the longer
games where the attack founders and Black wins the endgame are too
long for magazines. Watch...

We have arrived at a Sicilian by transposition from the
English; White has played Nc3 behind the c-pawn. White has more
space, which he will try to maintain by preventing Black from
playing freeing moves like ...b5. Then, when Black is passive and
White is fully developed, he will move to the attack.

Chess Quotes

"The technician, whose vocabulary has been doubled by Dr. Euwe, will find that White could have saved his soul by a desperado combination. Had this failure anything to do with the fact that Dr. Euwe's terminology was not yet existent at that time!?"